/*
 * Copyright (c) 1996, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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/*
 * (C) Copyright Taligent, Inc. 1996 - All Rights Reserved
 * (C) Copyright IBM Corp. 1996 - All Rights Reserved
 *
 *   The original version of this source code and documentation is copyrighted
 * and owned by Taligent, Inc., a wholly-owned subsidiary of IBM. These
 * materials are provided under terms of a License Agreement between Taligent
 * and Sun. This technology is protected by multiple US and International
 * patents. This notice and attribution to Taligent may not be removed.
 *   Taligent is a registered trademark of Taligent, Inc.
 *
 */

package java.text;

import java.io.InvalidObjectException;
import java.text.spi.DateFormatProvider;
import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;
import java.util.HashMap;
import java.util.Locale;
import java.util.Map;
import java.util.MissingResourceException;
import java.util.ResourceBundle;
import java.util.TimeZone;
import java.util.spi.LocaleServiceProvider;
import sun.util.locale.provider.LocaleProviderAdapter;
import sun.util.locale.provider.LocaleServiceProviderPool;

/**
 * {@code DateFormat} is an abstract class for date/time formatting subclasses which formats and
 * parses dates or time in a language-independent manner. The date/time formatting subclass, such as
 * {@link SimpleDateFormat}, allows for formatting (i.e., date &rarr; text), parsing (text &rarr;
 * date), and normalization.  The date is represented as a <code>Date</code> object or as the
 * milliseconds since January 1, 1970, 00:00:00 GMT.
 *
 * <p>{@code DateFormat} provides many class methods for obtaining default date/time formatters
 * based on the default or a given locale and a number of formatting styles. The formatting styles
 * include {@link #FULL}, {@link #LONG}, {@link #MEDIUM}, and {@link #SHORT}. More detail and
 * examples of using these styles are provided in the method descriptions.
 *
 * <p>{@code DateFormat} helps you to format and parse dates for any locale. Your code can be
 * completely independent of the locale conventions for months, days of the week, or even the
 * calendar format: lunar vs. solar.
 *
 * <p>To format a date for the current Locale, use one of the static factory methods: <blockquote>
 * <pre>{@code
 * myString = DateFormat.getDateInstance().format(myDate);
 * }</pre>
 * </blockquote> <p>If you are formatting multiple dates, it is more efficient to get the format and
 * use it multiple times so that the system doesn't have to fetch the information about the local
 * language and country conventions multiple times. <blockquote>
 * <pre>{@code
 * DateFormat df = DateFormat.getDateInstance();
 * for (int i = 0; i < myDate.length; ++i) {
 *     output.println(df.format(myDate[i]) + "; ");
 * }
 * }</pre>
 * </blockquote> <p>To format a date for a different Locale, specify it in the call to {@link
 * #getDateInstance(int, Locale) getDateInstance()}. <blockquote>
 * <pre>{@code
 * DateFormat df = DateFormat.getDateInstance(DateFormat.LONG, Locale.FRANCE);
 * }</pre>
 * </blockquote> <p>You can use a DateFormat to parse also. <blockquote>
 * <pre>{@code
 * myDate = df.parse(myString);
 * }</pre>
 * </blockquote> <p>Use {@code getDateInstance} to get the normal date format for that country.
 * There are other static factory methods available. Use {@code getTimeInstance} to get the time
 * format for that country. Use {@code getDateTimeInstance} to get a date and time format. You can
 * pass in different options to these factory methods to control the length of the result; from
 * {@link #SHORT} to {@link #MEDIUM} to {@link #LONG} to {@link #FULL}. The exact result depends on
 * the locale, but generally: <ul><li>{@link #SHORT} is completely numeric, such as {@code 12.13.52}
 * or {@code 3:30pm} <li>{@link #MEDIUM} is longer, such as {@code Jan 12, 1952} <li>{@link #LONG}
 * is longer, such as {@code January 12, 1952} or {@code 3:30:32pm} <li>{@link #FULL} is pretty
 * completely specified, such as {@code Tuesday, April 12, 1952 AD or 3:30:42pm PST}. </ul>
 *
 * <p>You can also set the time zone on the format if you wish. If you want even more control over
 * the format or parsing, (or want to give your users more control), you can try casting the {@code
 * DateFormat} you get from the factory methods to a {@link SimpleDateFormat}. This will work for
 * the majority of countries; just remember to put it in a {@code try} block in case you encounter
 * an unusual one.
 *
 * <p>You can also use forms of the parse and format methods with {@link ParsePosition} and {@link
 * FieldPosition} to allow you to <ul><li>progressively parse through pieces of a string. <li>align
 * any particular field, or find out where it is for selection on the screen. </ul>
 *
 * <h3><a name="synchronization">Synchronization</a></h3>
 *
 * <p> Date formats are not synchronized. It is recommended to create separate format instances for
 * each thread. If multiple threads access a format concurrently, it must be synchronized
 * externally.
 *
 * @author Mark Davis, Chen-Lieh Huang, Alan Liu
 * @see Format
 * @see NumberFormat
 * @see SimpleDateFormat
 * @see java.util.Calendar
 * @see java.util.GregorianCalendar
 * @see java.util.TimeZone
 */
public abstract class DateFormat extends Format {

  /**
   * The {@link Calendar} instance used for calculating the date-time fields
   * and the instant of time. This field is used for both formatting and
   * parsing.
   *
   * <p>Subclasses should initialize this field to a {@link Calendar}
   * appropriate for the {@link Locale} associated with this
   * <code>DateFormat</code>.
   *
   * @serial
   */
  protected Calendar calendar;

  /**
   * The number formatter that <code>DateFormat</code> uses to format numbers
   * in dates and times.  Subclasses should initialize this to a number format
   * appropriate for the locale associated with this <code>DateFormat</code>.
   *
   * @serial
   */
  protected NumberFormat numberFormat;

  /**
   * Useful constant for ERA field alignment.
   * Used in FieldPosition of date/time formatting.
   */
  public final static int ERA_FIELD = 0;
  /**
   * Useful constant for YEAR field alignment.
   * Used in FieldPosition of date/time formatting.
   */
  public final static int YEAR_FIELD = 1;
  /**
   * Useful constant for MONTH field alignment.
   * Used in FieldPosition of date/time formatting.
   */
  public final static int MONTH_FIELD = 2;
  /**
   * Useful constant for DATE field alignment.
   * Used in FieldPosition of date/time formatting.
   */
  public final static int DATE_FIELD = 3;
  /**
   * Useful constant for one-based HOUR_OF_DAY field alignment.
   * Used in FieldPosition of date/time formatting.
   * HOUR_OF_DAY1_FIELD is used for the one-based 24-hour clock.
   * For example, 23:59 + 01:00 results in 24:59.
   */
  public final static int HOUR_OF_DAY1_FIELD = 4;
  /**
   * Useful constant for zero-based HOUR_OF_DAY field alignment.
   * Used in FieldPosition of date/time formatting.
   * HOUR_OF_DAY0_FIELD is used for the zero-based 24-hour clock.
   * For example, 23:59 + 01:00 results in 00:59.
   */
  public final static int HOUR_OF_DAY0_FIELD = 5;
  /**
   * Useful constant for MINUTE field alignment.
   * Used in FieldPosition of date/time formatting.
   */
  public final static int MINUTE_FIELD = 6;
  /**
   * Useful constant for SECOND field alignment.
   * Used in FieldPosition of date/time formatting.
   */
  public final static int SECOND_FIELD = 7;
  /**
   * Useful constant for MILLISECOND field alignment.
   * Used in FieldPosition of date/time formatting.
   */
  public final static int MILLISECOND_FIELD = 8;
  /**
   * Useful constant for DAY_OF_WEEK field alignment.
   * Used in FieldPosition of date/time formatting.
   */
  public final static int DAY_OF_WEEK_FIELD = 9;
  /**
   * Useful constant for DAY_OF_YEAR field alignment.
   * Used in FieldPosition of date/time formatting.
   */
  public final static int DAY_OF_YEAR_FIELD = 10;
  /**
   * Useful constant for DAY_OF_WEEK_IN_MONTH field alignment.
   * Used in FieldPosition of date/time formatting.
   */
  public final static int DAY_OF_WEEK_IN_MONTH_FIELD = 11;
  /**
   * Useful constant for WEEK_OF_YEAR field alignment.
   * Used in FieldPosition of date/time formatting.
   */
  public final static int WEEK_OF_YEAR_FIELD = 12;
  /**
   * Useful constant for WEEK_OF_MONTH field alignment.
   * Used in FieldPosition of date/time formatting.
   */
  public final static int WEEK_OF_MONTH_FIELD = 13;
  /**
   * Useful constant for AM_PM field alignment.
   * Used in FieldPosition of date/time formatting.
   */
  public final static int AM_PM_FIELD = 14;
  /**
   * Useful constant for one-based HOUR field alignment.
   * Used in FieldPosition of date/time formatting.
   * HOUR1_FIELD is used for the one-based 12-hour clock.
   * For example, 11:30 PM + 1 hour results in 12:30 AM.
   */
  public final static int HOUR1_FIELD = 15;
  /**
   * Useful constant for zero-based HOUR field alignment.
   * Used in FieldPosition of date/time formatting.
   * HOUR0_FIELD is used for the zero-based 12-hour clock.
   * For example, 11:30 PM + 1 hour results in 00:30 AM.
   */
  public final static int HOUR0_FIELD = 16;
  /**
   * Useful constant for TIMEZONE field alignment.
   * Used in FieldPosition of date/time formatting.
   */
  public final static int TIMEZONE_FIELD = 17;

  // Proclaim serial compatibility with 1.1 FCS
  private static final long serialVersionUID = 7218322306649953788L;

  /**
   * Overrides Format.
   * Formats a time object into a time string. Examples of time objects
   * are a time value expressed in milliseconds and a Date object.
   *
   * @param obj must be a Number or a Date.
   * @param toAppendTo the string buffer for the returning time string.
   * @param fieldPosition keeps track of the position of the field within the returned string. On
   * input: an alignment field, if desired. On output: the offsets of the alignment field. For
   * example, given a time text "1996.07.10 AD at 15:08:56 PDT", if the given fieldPosition is
   * DateFormat.YEAR_FIELD, the begin index and end index of fieldPosition will be set to 0 and 4,
   * respectively. Notice that if the same time field appears more than once in a pattern, the
   * fieldPosition will be set for the first occurrence of that time field. For instance, formatting
   * a Date to the time string "1 PM PDT (Pacific Daylight Time)" using the pattern "h a z (zzzz)"
   * and the alignment field DateFormat.TIMEZONE_FIELD, the begin index and end index of
   * fieldPosition will be set to 5 and 8, respectively, for the first occurrence of the timezone
   * pattern character 'z'.
   * @return the string buffer passed in as toAppendTo, with formatted text appended.
   * @see java.text.Format
   */
  public final StringBuffer format(Object obj, StringBuffer toAppendTo,
      FieldPosition fieldPosition) {
    if (obj instanceof Date) {
      return format((Date) obj, toAppendTo, fieldPosition);
    } else if (obj instanceof Number) {
      return format(new Date(((Number) obj).longValue()),
          toAppendTo, fieldPosition);
    } else {
      throw new IllegalArgumentException("Cannot format given Object as a Date");
    }
  }

  /**
   * Formats a Date into a date/time string.
   *
   * @param date a Date to be formatted into a date/time string.
   * @param toAppendTo the string buffer for the returning date/time string.
   * @param fieldPosition keeps track of the position of the field within the returned string. On
   * input: an alignment field, if desired. On output: the offsets of the alignment field. For
   * example, given a time text "1996.07.10 AD at 15:08:56 PDT", if the given fieldPosition is
   * DateFormat.YEAR_FIELD, the begin index and end index of fieldPosition will be set to 0 and 4,
   * respectively. Notice that if the same time field appears more than once in a pattern, the
   * fieldPosition will be set for the first occurrence of that time field. For instance, formatting
   * a Date to the time string "1 PM PDT (Pacific Daylight Time)" using the pattern "h a z (zzzz)"
   * and the alignment field DateFormat.TIMEZONE_FIELD, the begin index and end index of
   * fieldPosition will be set to 5 and 8, respectively, for the first occurrence of the timezone
   * pattern character 'z'.
   * @return the string buffer passed in as toAppendTo, with formatted text appended.
   */
  public abstract StringBuffer format(Date date, StringBuffer toAppendTo,
      FieldPosition fieldPosition);

  /**
   * Formats a Date into a date/time string.
   *
   * @param date the time value to be formatted into a time string.
   * @return the formatted time string.
   */
  public final String format(Date date) {
    return format(date, new StringBuffer(),
        DontCareFieldPosition.INSTANCE).toString();
  }

  /**
   * Parses text from the beginning of the given string to produce a date.
   * The method may not use the entire text of the given string.
   * <p>
   * See the {@link #parse(String, ParsePosition)} method for more information
   * on date parsing.
   *
   * @param source A <code>String</code> whose beginning should be parsed.
   * @return A <code>Date</code> parsed from the string.
   * @throws ParseException if the beginning of the specified string cannot be parsed.
   */
  public Date parse(String source) throws ParseException {
    ParsePosition pos = new ParsePosition(0);
    Date result = parse(source, pos);
    if (pos.index == 0) {
      throw new ParseException("Unparseable date: \"" + source + "\"",
          pos.errorIndex);
    }
    return result;
  }

  /**
   * Parse a date/time string according to the given parse position.  For
   * example, a time text {@code "07/10/96 4:5 PM, PDT"} will be parsed into a {@code Date}
   * that is equivalent to {@code Date(837039900000L)}.
   *
   * <p> By default, parsing is lenient: If the input is not in the form used
   * by this object's format method but can still be parsed as a date, then
   * the parse succeeds.  Clients may insist on strict adherence to the
   * format by calling {@link #setLenient(boolean) setLenient(false)}.
   *
   * <p>This parsing operation uses the {@link #calendar} to produce
   * a {@code Date}. As a result, the {@code calendar}'s date-time
   * fields and the {@code TimeZone} value may have been
   * overwritten, depending on subclass implementations. Any {@code
   * TimeZone} value that has previously been set by a call to
   * {@link #setTimeZone(java.util.TimeZone) setTimeZone} may need
   * to be restored for further operations.
   *
   * @param source The date/time string to be parsed
   * @param pos On input, the position at which to start parsing; on output, the position at which
   * parsing terminated, or the start position if the parse failed.
   * @return A {@code Date}, or {@code null} if the input could not be parsed
   */
  public abstract Date parse(String source, ParsePosition pos);

  /**
   * Parses text from a string to produce a <code>Date</code>.
   * <p>
   * The method attempts to parse text starting at the index given by
   * <code>pos</code>.
   * If parsing succeeds, then the index of <code>pos</code> is updated
   * to the index after the last character used (parsing does not necessarily
   * use all characters up to the end of the string), and the parsed
   * date is returned. The updated <code>pos</code> can be used to
   * indicate the starting point for the next call to this method.
   * If an error occurs, then the index of <code>pos</code> is not
   * changed, the error index of <code>pos</code> is set to the index of
   * the character where the error occurred, and null is returned.
   * <p>
   * See the {@link #parse(String, ParsePosition)} method for more information
   * on date parsing.
   *
   * @param source A <code>String</code>, part of which should be parsed.
   * @param pos A <code>ParsePosition</code> object with index and error index information as
   * described above.
   * @return A <code>Date</code> parsed from the string. In case of error, returns null.
   * @throws NullPointerException if <code>pos</code> is null.
   */
  public Object parseObject(String source, ParsePosition pos) {
    return parse(source, pos);
  }

  /**
   * Constant for full style pattern.
   */
  public static final int FULL = 0;
  /**
   * Constant for long style pattern.
   */
  public static final int LONG = 1;
  /**
   * Constant for medium style pattern.
   */
  public static final int MEDIUM = 2;
  /**
   * Constant for short style pattern.
   */
  public static final int SHORT = 3;
  /**
   * Constant for default style pattern.  Its value is MEDIUM.
   */
  public static final int DEFAULT = MEDIUM;

  /**
   * Gets the time formatter with the default formatting style
   * for the default {@link java.util.Locale.Category#FORMAT FORMAT} locale.
   * <p>This is equivalent to calling
   * {@link #getTimeInstance(int, Locale) getTimeInstance(DEFAULT,
   * Locale.getDefault(Locale.Category.FORMAT))}.
   *
   * @return a time formatter.
   * @see java.util.Locale#getDefault(java.util.Locale.Category)
   * @see java.util.Locale.Category#FORMAT
   */
  public final static DateFormat getTimeInstance() {
    return get(DEFAULT, 0, 1, Locale.getDefault(Locale.Category.FORMAT));
  }

  /**
   * Gets the time formatter with the given formatting style
   * for the default {@link java.util.Locale.Category#FORMAT FORMAT} locale.
   * <p>This is equivalent to calling
   * {@link #getTimeInstance(int, Locale) getTimeInstance(style,
   * Locale.getDefault(Locale.Category.FORMAT))}.
   *
   * @param style the given formatting style. For example, SHORT for "h:mm a" in the US locale.
   * @return a time formatter.
   * @see java.util.Locale#getDefault(java.util.Locale.Category)
   * @see java.util.Locale.Category#FORMAT
   */
  public final static DateFormat getTimeInstance(int style) {
    return get(style, 0, 1, Locale.getDefault(Locale.Category.FORMAT));
  }

  /**
   * Gets the time formatter with the given formatting style
   * for the given locale.
   *
   * @param style the given formatting style. For example, SHORT for "h:mm a" in the US locale.
   * @param aLocale the given locale.
   * @return a time formatter.
   */
  public final static DateFormat getTimeInstance(int style,
      Locale aLocale) {
    return get(style, 0, 1, aLocale);
  }

  /**
   * Gets the date formatter with the default formatting style
   * for the default {@link java.util.Locale.Category#FORMAT FORMAT} locale.
   * <p>This is equivalent to calling
   * {@link #getDateInstance(int, Locale) getDateInstance(DEFAULT,
   * Locale.getDefault(Locale.Category.FORMAT))}.
   *
   * @return a date formatter.
   * @see java.util.Locale#getDefault(java.util.Locale.Category)
   * @see java.util.Locale.Category#FORMAT
   */
  public final static DateFormat getDateInstance() {
    return get(0, DEFAULT, 2, Locale.getDefault(Locale.Category.FORMAT));
  }

  /**
   * Gets the date formatter with the given formatting style
   * for the default {@link java.util.Locale.Category#FORMAT FORMAT} locale.
   * <p>This is equivalent to calling
   * {@link #getDateInstance(int, Locale) getDateInstance(style,
   * Locale.getDefault(Locale.Category.FORMAT))}.
   *
   * @param style the given formatting style. For example, SHORT for "M/d/yy" in the US locale.
   * @return a date formatter.
   * @see java.util.Locale#getDefault(java.util.Locale.Category)
   * @see java.util.Locale.Category#FORMAT
   */
  public final static DateFormat getDateInstance(int style) {
    return get(0, style, 2, Locale.getDefault(Locale.Category.FORMAT));
  }

  /**
   * Gets the date formatter with the given formatting style
   * for the given locale.
   *
   * @param style the given formatting style. For example, SHORT for "M/d/yy" in the US locale.
   * @param aLocale the given locale.
   * @return a date formatter.
   */
  public final static DateFormat getDateInstance(int style,
      Locale aLocale) {
    return get(0, style, 2, aLocale);
  }

  /**
   * Gets the date/time formatter with the default formatting style
   * for the default {@link java.util.Locale.Category#FORMAT FORMAT} locale.
   * <p>This is equivalent to calling
   * {@link #getDateTimeInstance(int, int, Locale) getDateTimeInstance(DEFAULT,
   * DEFAULT, Locale.getDefault(Locale.Category.FORMAT))}.
   *
   * @return a date/time formatter.
   * @see java.util.Locale#getDefault(java.util.Locale.Category)
   * @see java.util.Locale.Category#FORMAT
   */
  public final static DateFormat getDateTimeInstance() {
    return get(DEFAULT, DEFAULT, 3, Locale.getDefault(Locale.Category.FORMAT));
  }

  /**
   * Gets the date/time formatter with the given date and time
   * formatting styles for the default {@link java.util.Locale.Category#FORMAT FORMAT} locale.
   * <p>This is equivalent to calling
   * {@link #getDateTimeInstance(int, int, Locale) getDateTimeInstance(dateStyle,
   * timeStyle, Locale.getDefault(Locale.Category.FORMAT))}.
   *
   * @param dateStyle the given date formatting style. For example, SHORT for "M/d/yy" in the US
   * locale.
   * @param timeStyle the given time formatting style. For example, SHORT for "h:mm a" in the US
   * locale.
   * @return a date/time formatter.
   * @see java.util.Locale#getDefault(java.util.Locale.Category)
   * @see java.util.Locale.Category#FORMAT
   */
  public final static DateFormat getDateTimeInstance(int dateStyle,
      int timeStyle) {
    return get(timeStyle, dateStyle, 3, Locale.getDefault(Locale.Category.FORMAT));
  }

  /**
   * Gets the date/time formatter with the given formatting styles
   * for the given locale.
   *
   * @param dateStyle the given date formatting style.
   * @param timeStyle the given time formatting style.
   * @param aLocale the given locale.
   * @return a date/time formatter.
   */
  public final static DateFormat
  getDateTimeInstance(int dateStyle, int timeStyle, Locale aLocale) {
    return get(timeStyle, dateStyle, 3, aLocale);
  }

  /**
   * Get a default date/time formatter that uses the SHORT style for both the
   * date and the time.
   *
   * @return a date/time formatter
   */
  public final static DateFormat getInstance() {
    return getDateTimeInstance(SHORT, SHORT);
  }

  /**
   * Returns an array of all locales for which the
   * <code>get*Instance</code> methods of this class can return
   * localized instances.
   * The returned array represents the union of locales supported by the Java
   * runtime and by installed
   * {@link java.text.spi.DateFormatProvider DateFormatProvider} implementations.
   * It must contain at least a <code>Locale</code> instance equal to
   * {@link java.util.Locale#US Locale.US}.
   *
   * @return An array of locales for which localized <code>DateFormat</code> instances are
   * available.
   */
  public static Locale[] getAvailableLocales() {
    LocaleServiceProviderPool pool =
        LocaleServiceProviderPool.getPool(DateFormatProvider.class);
    return pool.getAvailableLocales();
  }

  /**
   * Set the calendar to be used by this date format.  Initially, the default
   * calendar for the specified or default locale is used.
   *
   * <p>Any {@link java.util.TimeZone TimeZone} and {@linkplain
   * #isLenient() leniency} values that have previously been set are
   * overwritten by {@code newCalendar}'s values.
   *
   * @param newCalendar the new {@code Calendar} to be used by the date format
   */
  public void setCalendar(Calendar newCalendar) {
    this.calendar = newCalendar;
  }

  /**
   * Gets the calendar associated with this date/time formatter.
   *
   * @return the calendar associated with this date/time formatter.
   */
  public Calendar getCalendar() {
    return calendar;
  }

  /**
   * Allows you to set the number formatter.
   *
   * @param newNumberFormat the given new NumberFormat.
   */
  public void setNumberFormat(NumberFormat newNumberFormat) {
    this.numberFormat = newNumberFormat;
  }

  /**
   * Gets the number formatter which this date/time formatter uses to
   * format and parse a time.
   *
   * @return the number formatter which this date/time formatter uses.
   */
  public NumberFormat getNumberFormat() {
    return numberFormat;
  }

  /**
   * Sets the time zone for the calendar of this {@code DateFormat} object.
   * This method is equivalent to the following call.
   * <blockquote><pre>{@code
   * getCalendar().setTimeZone(zone)
   * }</pre></blockquote>
   *
   * <p>The {@code TimeZone} set by this method is overwritten by a
   * {@link #setCalendar(java.util.Calendar) setCalendar} call.
   *
   * <p>The {@code TimeZone} set by this method may be overwritten as
   * a result of a call to the parse method.
   *
   * @param zone the given new time zone.
   */
  public void setTimeZone(TimeZone zone) {
    calendar.setTimeZone(zone);
  }

  /**
   * Gets the time zone.
   * This method is equivalent to the following call.
   * <blockquote><pre>{@code
   * getCalendar().getTimeZone()
   * }</pre></blockquote>
   *
   * @return the time zone associated with the calendar of DateFormat.
   */
  public TimeZone getTimeZone() {
    return calendar.getTimeZone();
  }

  /**
   * Specify whether or not date/time parsing is to be lenient.  With
   * lenient parsing, the parser may use heuristics to interpret inputs that
   * do not precisely match this object's format.  With strict parsing,
   * inputs must match this object's format.
   *
   * <p>This method is equivalent to the following call.
   * <blockquote><pre>{@code
   * getCalendar().setLenient(lenient)
   * }</pre></blockquote>
   *
   * <p>This leniency value is overwritten by a call to {@link
   * #setCalendar(java.util.Calendar) setCalendar()}.
   *
   * @param lenient when {@code true}, parsing is lenient
   * @see java.util.Calendar#setLenient(boolean)
   */
  public void setLenient(boolean lenient) {
    calendar.setLenient(lenient);
  }

  /**
   * Tell whether date/time parsing is to be lenient.
   * This method is equivalent to the following call.
   * <blockquote><pre>{@code
   * getCalendar().isLenient()
   * }</pre></blockquote>
   *
   * @return {@code true} if the {@link #calendar} is lenient; {@code false} otherwise.
   * @see java.util.Calendar#isLenient()
   */
  public boolean isLenient() {
    return calendar.isLenient();
  }

  /**
   * Overrides hashCode
   */
  public int hashCode() {
    return numberFormat.hashCode();
    // just enough fields for a reasonable distribution
  }

  /**
   * Overrides equals
   */
  public boolean equals(Object obj) {
    if (this == obj) {
      return true;
    }
    if (obj == null || getClass() != obj.getClass()) {
      return false;
    }
    DateFormat other = (DateFormat) obj;
    return (// calendar.equivalentTo(other.calendar) // THIS API DOESN'T EXIST YET!
        calendar.getFirstDayOfWeek() == other.calendar.getFirstDayOfWeek() &&
            calendar.getMinimalDaysInFirstWeek() == other.calendar.getMinimalDaysInFirstWeek() &&
            calendar.isLenient() == other.calendar.isLenient() &&
            calendar.getTimeZone().equals(other.calendar.getTimeZone()) &&
            numberFormat.equals(other.numberFormat));
  }

  /**
   * Overrides Cloneable
   */
  public Object clone() {
    DateFormat other = (DateFormat) super.clone();
    other.calendar = (Calendar) calendar.clone();
    other.numberFormat = (NumberFormat) numberFormat.clone();
    return other;
  }

  /**
   * Creates a DateFormat with the given time and/or date style in the given
   * locale.
   *
   * @param timeStyle a value from 0 to 3 indicating the time format, ignored if flags is 2
   * @param dateStyle a value from 0 to 3 indicating the time format, ignored if flags is 1
   * @param flags either 1 for a time format, 2 for a date format, or 3 for a date/time format
   * @param loc the locale for the format
   */
  private static DateFormat get(int timeStyle, int dateStyle,
      int flags, Locale loc) {
    if ((flags & 1) != 0) {
      if (timeStyle < 0 || timeStyle > 3) {
        throw new IllegalArgumentException("Illegal time style " + timeStyle);
      }
    } else {
      timeStyle = -1;
    }
    if ((flags & 2) != 0) {
      if (dateStyle < 0 || dateStyle > 3) {
        throw new IllegalArgumentException("Illegal date style " + dateStyle);
      }
    } else {
      dateStyle = -1;
    }

    LocaleProviderAdapter adapter = LocaleProviderAdapter.getAdapter(DateFormatProvider.class, loc);
    DateFormat dateFormat = get(adapter, timeStyle, dateStyle, loc);
    if (dateFormat == null) {
      dateFormat = get(LocaleProviderAdapter.forJRE(), timeStyle, dateStyle, loc);
    }
    return dateFormat;
  }

  private static DateFormat get(LocaleProviderAdapter adapter, int timeStyle, int dateStyle,
      Locale loc) {
    DateFormatProvider provider = adapter.getDateFormatProvider();
    DateFormat dateFormat;
    if (timeStyle == -1) {
      dateFormat = provider.getDateInstance(dateStyle, loc);
    } else {
      if (dateStyle == -1) {
        dateFormat = provider.getTimeInstance(timeStyle, loc);
      } else {
        dateFormat = provider.getDateTimeInstance(dateStyle, timeStyle, loc);
      }
    }
    return dateFormat;
  }

  /**
   * Create a new date format.
   */
  protected DateFormat() {
  }

  /**
   * Defines constants that are used as attribute keys in the
   * <code>AttributedCharacterIterator</code> returned
   * from <code>DateFormat.formatToCharacterIterator</code> and as
   * field identifiers in <code>FieldPosition</code>.
   * <p>
   * The class also provides two methods to map
   * between its constants and the corresponding Calendar constants.
   *
   * @see java.util.Calendar
   * @since 1.4
   */
  public static class Field extends Format.Field {

    // Proclaim serial compatibility with 1.4 FCS
    private static final long serialVersionUID = 7441350119349544720L;

    // table of all instances in this class, used by readResolve
    private static final Map<String, Field> instanceMap = new HashMap<>(18);
    // Maps from Calendar constant (such as Calendar.ERA) to Field
    // constant (such as Field.ERA).
    private static final Field[] calendarToFieldMapping =
        new Field[Calendar.FIELD_COUNT];

    /**
     * Calendar field.
     */
    private int calendarField;

    /**
     * Returns the <code>Field</code> constant that corresponds to
     * the <code>Calendar</code> constant <code>calendarField</code>.
     * If there is no direct mapping between the <code>Calendar</code>
     * constant and a <code>Field</code>, null is returned.
     *
     * @param calendarField Calendar field constant
     * @return Field instance representing calendarField.
     * @throws IllegalArgumentException if <code>calendarField</code> is not the value of a
     * <code>Calendar</code> field constant.
     * @see java.util.Calendar
     */
    public static Field ofCalendarField(int calendarField) {
      if (calendarField < 0 || calendarField >=
          calendarToFieldMapping.length) {
        throw new IllegalArgumentException("Unknown Calendar constant "
            + calendarField);
      }
      return calendarToFieldMapping[calendarField];
    }

    /**
     * Creates a <code>Field</code>.
     *
     * @param name the name of the <code>Field</code>
     * @param calendarField the <code>Calendar</code> constant this <code>Field</code> corresponds
     * to; any value, even one outside the range of legal <code>Calendar</code> values may be used,
     * but <code>-1</code> should be used for values that don't correspond to legal
     * <code>Calendar</code> values
     */
    protected Field(String name, int calendarField) {
      super(name);
      this.calendarField = calendarField;
      if (this.getClass() == DateFormat.Field.class) {
        instanceMap.put(name, this);
        if (calendarField >= 0) {
          // assert(calendarField < Calendar.FIELD_COUNT);
          calendarToFieldMapping[calendarField] = this;
        }
      }
    }

    /**
     * Returns the <code>Calendar</code> field associated with this
     * attribute. For example, if this represents the hours field of
     * a <code>Calendar</code>, this would return
     * <code>Calendar.HOUR</code>. If there is no corresponding
     * <code>Calendar</code> constant, this will return -1.
     *
     * @return Calendar constant for this field
     * @see java.util.Calendar
     */
    public int getCalendarField() {
      return calendarField;
    }

    /**
     * Resolves instances being deserialized to the predefined constants.
     *
     * @return resolved DateFormat.Field constant
     * @throws InvalidObjectException if the constant could not be resolved.
     */
    @Override
    protected Object readResolve() throws InvalidObjectException {
      if (this.getClass() != DateFormat.Field.class) {
        throw new InvalidObjectException("subclass didn't correctly implement readResolve");
      }

      Object instance = instanceMap.get(getName());
      if (instance != null) {
        return instance;
      } else {
        throw new InvalidObjectException("unknown attribute name");
      }
    }

    //
    // The constants
    //

    /**
     * Constant identifying the era field.
     */
    public final static Field ERA = new Field("era", Calendar.ERA);

    /**
     * Constant identifying the year field.
     */
    public final static Field YEAR = new Field("year", Calendar.YEAR);

    /**
     * Constant identifying the month field.
     */
    public final static Field MONTH = new Field("month", Calendar.MONTH);

    /**
     * Constant identifying the day of month field.
     */
    public final static Field DAY_OF_MONTH = new
        Field("day of month", Calendar.DAY_OF_MONTH);

    /**
     * Constant identifying the hour of day field, where the legal values
     * are 1 to 24.
     */
    public final static Field HOUR_OF_DAY1 = new Field("hour of day 1", -1);

    /**
     * Constant identifying the hour of day field, where the legal values
     * are 0 to 23.
     */
    public final static Field HOUR_OF_DAY0 = new
        Field("hour of day", Calendar.HOUR_OF_DAY);

    /**
     * Constant identifying the minute field.
     */
    public final static Field MINUTE = new Field("minute", Calendar.MINUTE);

    /**
     * Constant identifying the second field.
     */
    public final static Field SECOND = new Field("second", Calendar.SECOND);

    /**
     * Constant identifying the millisecond field.
     */
    public final static Field MILLISECOND = new
        Field("millisecond", Calendar.MILLISECOND);

    /**
     * Constant identifying the day of week field.
     */
    public final static Field DAY_OF_WEEK = new
        Field("day of week", Calendar.DAY_OF_WEEK);

    /**
     * Constant identifying the day of year field.
     */
    public final static Field DAY_OF_YEAR = new
        Field("day of year", Calendar.DAY_OF_YEAR);

    /**
     * Constant identifying the day of week field.
     */
    public final static Field DAY_OF_WEEK_IN_MONTH =
        new Field("day of week in month",
            Calendar.DAY_OF_WEEK_IN_MONTH);

    /**
     * Constant identifying the week of year field.
     */
    public final static Field WEEK_OF_YEAR = new
        Field("week of year", Calendar.WEEK_OF_YEAR);

    /**
     * Constant identifying the week of month field.
     */
    public final static Field WEEK_OF_MONTH = new
        Field("week of month", Calendar.WEEK_OF_MONTH);

    /**
     * Constant identifying the time of day indicator
     * (e.g. "a.m." or "p.m.") field.
     */
    public final static Field AM_PM = new
        Field("am pm", Calendar.AM_PM);

    /**
     * Constant identifying the hour field, where the legal values are
     * 1 to 12.
     */
    public final static Field HOUR1 = new Field("hour 1", -1);

    /**
     * Constant identifying the hour field, where the legal values are
     * 0 to 11.
     */
    public final static Field HOUR0 = new
        Field("hour", Calendar.HOUR);

    /**
     * Constant identifying the time zone field.
     */
    public final static Field TIME_ZONE = new Field("time zone", -1);
  }
}
